In a tape drive, such as a linear tape drive, information is stored to and read from magnetic tape media. In general, the tape media will include a number of data tracks spaced laterally across the tape. These data tracks on the tape are usually grouped into a number of logical bands. Within each logical band are a number of sub-bands. For example, as shown in background FIG. 1, tape architecture 100 includes 4 logical bands 101-104 with each logical band including 4 sub-bands (111-114). Further, each sub-band includes a number of tracks. For example, sub-band 111 is shown broken down into 4 tracks (121-124). Although 4 logical bands, 4 sub-bands and 4 tracks are shown, it is merely for purposes of clarity in the description and Figure. Other numbers of logical bands, sub-bands and/or tracks may also be utilized.
In the present tape architecture, as shown by the arrows on tracks 121-124 of sub-band 111, some of the tracks (e.g., 121 and 122) are accessible when the tape is traveling in the forward direction and some of the tracks (e.g., 123 and 124) are accessible when the tape is traveling in the reverse direction. In other words, the present tape architecture orients each of the tracks within a sub band in a “serpentine” fashion.
The head architecture typically includes multiple channels that write and read data in a logical band, with a single channel for each data sub band. In general, a channel on the head refers to a reader and a writer, separated longitudinally. For example, when the tape travels in a forward direction across the head, the reader and writer would be in a first orientation. That is, the writer would be the first portion to encounter the track and the reader would be positioned to approach the data track after the writer.
However, when the tape travels in reverse across the head, the reader and writer would need to be in a second orientation. That is, the writer would again have to be the first to encounter the track and the reader would again need to be positioned after the writer.
Because of the need to have readers and writers in two orientations, multiple channel head architecture typically includes multiple readers and/or writers for each sub band. Drives using thin-film head technology usually have at least two readers and at least two writers per sub band, with one writer and one reader used when the tape is moving in one direction and the other reader and the other writer are used when the tape is moving in the opposite direction. Some tape drives have two of one and one of the other, for example two readers and one writer or one reader and two writers, with the single element centered longitudinally between the other two and is used when the tape is moving in both directions.
In at least one previously used head architecture, the separated readers and writers were laterally interleaved (except for the outside most reader or writer). That is, each reader which would be used when the tape was moving in one direction was located between two of the writers that would be used when the tape was moving in the opposite direction. Likewise, each writer which would be used when the tape was moving in one direction was located between two of the readers that would be used when the tape was moving in the opposite direction. The elements at the lateral edges of the cluster would of course not be between other elements.
In order to access all of the tracks within each sub bands, for example sub bands 111-114 of FIG. 1, the head is mounted on an actuator that moves it laterally across the tape. For example, the head would be in one location to write data track 121, would move to another location to write track 123 after the direction of tape motion was reversed. The head would move to another location to write track 122. Alternately, the head could be fabricated with offset elements so that the head location to write tracks 121 and 123, for example, could be the same, but the head would move to a different location to write tracks 122 and 124.
The active read/write portions of the head are typically manufactured to be the same size as one logical band. For example, if the logical band has 7 sub-bands, then the head will include 7 multiple channels which will match up to the 7 sub-bands and which will fill the entire logical band. Since the readers and writers are on the same part of the head, that is, covering a single logical band, a head actuator must be able to move the head not only to access the different tracks within a sub-band but also so that the readers and writers can access every logical band on the tape. This is the case whether there and two read elements and two write elements per channel, or if there are two of one and one of the other as described above, or if the read elements and the write elements are interleaved. Thus, in the example shown in FIG. 1 which shows 4 logical bands, the head must necessarily be able to travel approximately three-quarters of the tape width to ensure access to every data track in every logical band. For purposes of clarity, head travel is hereinafter referred to as ‘stroke’.